1. Field of the Invention
The invention relates to electric toothbrushes.
2. Description of Prior Art
Many toothbrushes are known and widely used having a set of bristles mounted to a brush head that is driven by an electric motor inside a toothbrush handle. The motor may be powered by a battery, also inside the handle, or from a power supply socket adjacent a point-of-use. As such, the brush head can be rotated and/or vibrated by the motor to enhance the operation of the toothbrush for cleaning teeth. For vibrating the brush head, it is already known to provide an eccentrically mounted weight inside the handle directly coupled to the motor. As a result the handle is vibrated and this vibration is transmitted to the brush head in use via a shank of the toothbrush. This means that the user""s hand is vibrated. Inherently the vibrations are dampened by the user""s grip. When using the toothbrush, the handle vibrations are not comfortable for the user and waste, in effect, considerable mechanical energy that must be supplied by the motor.
It is also known in U.S. Pat. No. 5,987,681 to mount an unbalanced mass on the drive shaft near a brush head but movement of a shank of the toothbrush also uses up, or wastes, energy that must be provided by the motor.
It is an object of the invention to overcome or to at least reduce these problems.
According to the invention there is provided an electric toothbrush having an elongate handle, an electric motor inside the handle, a drive shaft rotatable about a longitudinal axis of the toothbrush inside an elongate shank a brush head mounted at a remote end of the shank carrying bristles extending general transversely to the longitudinal axis from the brush head, a drive shaft extension formed with a balanced mass freely rotatable within a cavity in the brush head about said longitudinal axis, and an axle having an axis is off-set from the longitudinal axis which mechanically couples the brush head to a remote end of the drive shaft extension, in which the brush head is flexibly coupled to the remote end of the shank, such that when the drive shaft is rotated the brush head is caused to vibrate relative to the shank.
The drive shaft may be supported by a bearing, on the longitudinal axis, that is mounted adjacent the remote end of the shank.
The shaft extension may comprise a shaft rotatable about the longitudinal axis and a uniform sleeve that fits over the shaft to form the balanced mass.
The sleeve is preferably made of metal.
The brush head and the remote end of the shank may be flexibly coupled together by a coupling formed by integrally formed resilient engaging formations on mating surfaces of the brush head and the remote end of the shank, and a resilient O-ring separating the mating surfaces.
A resilient tube may be provided that drivingly connects the shaft extension to the drive shaft.
The drive shaft and the drive shaft extension may be integrally formed.